Intravascular imaging and endovascular surgery have increased the life expectancy and quality of life for patients suffering from cardiovascular disease. Imaging techniques such as intravascular ultrasound (IVUS), intravascular Doppler, and intravascular optical coherence tomography (OCT) allow radiologists, neurologists, neurosurgeons, cardiologists, vascular surgeons, etc., to directly visualize a patient's vasculature to observe occlusions, thrombi, embolisms, aneurisms, etc. Coupling the imaging techniques with advanced surgical procedures, it is possible to counteract cardiovascular disease by removing thrombi or placing stents in weakened vessels. Using such procedures, a patient at high risk for cardiac arrest can have the risk lessened, and experience a better quality of life after treatment. Furthermore, because intravascular imaging and endovascular surgery are less invasive than techniques such as coronary bypass, the risk of surgical complication is greatly reduced and hospital stays and recovery times are shortened.
While the procedures are non-invasive, the substantial distance between the entry into the body and the targeted tissue makes the procedures complex. Vascular access for an imaging catheter is gained through an arterial entry point such as the radial, brachial, or femoral artery. From the entry point, a provider can access the vasculature of most important organs (heart, lungs, kidneys, brain) by guiding the catheter along a placed guide wire to a feature of interest. Because there is some amount of travel between the entry point and the target, an additional imaging technique, such as angiography, is needed to determine the approximate position of the guide wire and/or catheter within the body.
Because the two imaging systems (intravascular imaging and angiography) are operated independently, it can be difficult to precisely locate imaged intravascular tissues within the body. A cardiologist will typically place a guide wire in the vasculature while observing the angiogram, moving the guide wire so that the distal end of the guide wire is approximately adjacent to a feature of interest. Once the guide wire is placed, the cardiologist will deliver the imaging catheter by pushing the catheter to a stop at the distal end of the guide wire. Logically, the subsequent tissue images, e.g., IVUS images, must be approximately located at the distal end of the guide wire, which was visualized previously using the angiogram. In some cases, when the location of the image is unclear, additional contrast and x-ray imaging are used to locate the catheter, which shows up in the angiogram as a pattern of shadows.
In many cases, the exact location of a tissue image within a body is not known, however, because the imaging plane of the image collector (e.g., ultrasound collector) is not well defined with respect to the distal end of the guide wire. This problem is especially acute when using advanced pullback imaging catheters that can be move longitudinally within the catheter once deployed. Because the image collector is very small, the shadow of the guide wire can make it difficult to locate the precise position of the image collector within the sensor package during translation. Furthermore, if a feature of concern is found while translating the image collector, it can be difficult to pinpoint the location of the feature without stopping the translation and adding additional contrast and x-rays. Unfortunately, angiography presents risks to both the patient and the provider. Angiography uses radiopaque contrast agents and x-ray imaging, e.g., fluoroscopy, to image the vasculature. Because the images are taken in real time, substantially greater amounts of x-ray radiation are required as compared to a radiograph (x-ray picture). In addition to the x-ray exposure, patients may suffer side effects from the radiopaque contrast agents, including pain, adverse drug interactions, and renal failure. For technicians and physicians, there are also risks of x-ray exposure as well as orthopedic injuries (e.g., lower back strain) due to the extra weight of the lead-lined aprons and other protective equipment.
Thus, there is a need for improved methods of locating an image produced by an image catheter during a procedure. Any improvement that decreases the time of a procedure using angiography will benefit both doctor and patient.